Downlink OFDMA for service sets with mixed client types

ABSTRACT

Techniques are provided herein to allow a wireless network access point (AP) to more fully use its bandwidth in order to leverage the different bandwidth capabilities of different types of wireless client devices that the AP serves. The AP generates control parameters for usage of a plurality of channels in a bandwidth during a downlink transmission interval. The control parameters comprise information indicating channel assignments that result in multiple downlink transmissions that at least partially overlap in time to different wireless client devices according to their respective bandwidth capabilities. The AP transmits the control parameters in a control frame in advance of the downlink transmission interval on each of the plurality of channels in the bandwidth.

RELATED APPLICATION

This application is a continuation of U.S. Non-Provisional applicationSer. No. 12/819,327, filed Jun. 21, 2010, which in turn claims priorityto U.S. Provisional Patent Application No. 61/312,633, filed Mar. 10,2010. The entirety of each of these applications is incorporated hereinby reference.

TECHNICAL FIELD

The present disclosure relates to wireless local area networks and moreparticularly to better use spectrum available to a wireless access point(AP) that services a Basic Service Set (BSS) comprising a mix ofdifferent types of client devices.

BACKGROUND

In a wireless local area network (WLAN), such as an IEEE 802.11 WLAN,future networks will allocate wider bandwidth channels, e.g., 80 MHz ormore, to individual client devices. In sparse home WLAN deployments,this can be quite advantageous. The wider bandwidth channel is valuabledue to the additional speed it offers, but this benefit may gounrealized if the bandwidth is not fully used. For example, some legacy802.11 client devices can support only 20 or 40 MHz channels and theirpresence in the network can block the full use of the wider bandwidth bymore current (higher bandwidth) client devices. In the worse case, atransmission for a single 20 MHz channel client device could block allother client devices (that are capable of operating with wider bandwidthchannels) in the same BSS from accessing the remaining bandwidthavailable to the AP during the transmission (e.g., 60 MHz), making the80 MHz or wider channel not fully used in a home or enterprisedeployment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an example of a wireless networkdeployment in which a wireless network access point (AP) device isserving multiple client devices of different bandwidth capabilities ortypes.

FIG. 2 is a diagram showing how spectrum usage of an AP device serving aplurality of different types of client devices can be improved using thetechniques described herein.

FIG. 3 is an example of a block diagram of an AP device configured tomore fully use the spectrum when serving a plurality of client devicesof different types.

FIG. 4 is an example of a flow chart showing the operations of the APdevice configured to more fully use the spectrum when serving aplurality of client devices of different types.

FIG. 5 is a spectrum usage and timing diagram showing one example bywhich an AP is configured to more fully use the spectrum across multiplechannels when serving a plurality of client devices of different types.

FIG. 6 is a diagram illustrating an example of a control frame that theAP transmits to notify client devices of a spectrum usage scenario for adownlink transmission session according to the techniques describedherein.

FIG. 7 is an example of a diagram of a packet header for one of thefields in a data frame shown in FIG. 5.

FIG. 8 is a spectrum usage and timing diagram of another example bywhich an AP is configured to more fully use the spectrum across multiplechannels when serving a plurality of client devices of different types.

DESCRIPTION OF EXAMPLE EMBODIMENTS Overview

Techniques are provided herein to allow a wireless network access point(AP) to more fully use the bandwidth in order to compensate for and toleverage the different bandwidth capabilities of different types ofwireless client devices that the AP serves. The AP generates controlparameters for usage of a plurality of individual channels in abandwidth during a downlink transmission interval. The individualchannels may be viewed as “subchannels” with respect to the overallbandwidth, and for this reason, the term subchannel is used herein torefer to an individual channel. The control parameters compriseinformation indicating channel assignments for multiple downlinktransmissions that at least partially overlap in time to differentwireless client devices according to their respective bandwidthcapabilities and information indicating timing for transmissions ofacknowledgment messages by client devices to the access point. The APtransmits the control parameters in a control frame in advance of thedownlink transmission interval on each of the plurality of channels inthe bandwidth.

The downlink frames to different types of client device overlap, atleast partially in time, and as a result, the AP is more fully using itsavailable bandwidth. The mechanism described herein operates in a mannersimilar to orthogonal frequency division multiple access (OFDMA)techniques, albeit coarsely, across different subchannels (e.g., 20 MHzsubchannels) and is therefore referred to herein as a downlink-OFDMAtechnique, or DL-OFMDA.

Example Embodiments

Referring first to FIG. 1, a wireless network environment is shown atreference numeral 5 comprising a wireless access point (AP) 10 and aplurality of client devices (CDs), e.g., CDs 20(1)-20(N). The AP 10 andthe CDs 20(1)-20(N) are configured to perform wireless communicationaccording to a wireless network communication protocol such as the IEEE802.11 wireless local area network (WLAN) communication protocol, knowncommercially as WiFi™. The CDs are also referred to herein as “stations”or “STAs”.

In a given network deployment, the AP 10 may be called upon to serve avariety of different types of client devices that have differentbandwidth capabilities. A network deployment may involve older types ofclient devices that were designed to operate according to rules of the802.11 standard that have since been improved upon in later versions toallow for better performance (higher throughput) and fuller usage of thespectrum. The different versions of the 802.11 standard involvedifferent modulation schemes and also different usage capabilities ofthe spectrum. That is, IEEE 801.11n standard and the future 802.11acstandard allow for multiple adjacent channels to be bonded together toform a single wider bandwidth channel, which allows for very highthroughput. Future 802.11ac devices may even operate on two non-adjacentsets of bonded channels; e.g. to form 160 MHz from two 80 MHz segments.For example, a network deployment may include 802.11a/g client devices,802.11n client devices, and soon in the future, 802.11ac client devices.

It is common today, and also inevitable in the future, that a given APwill be serving a plurality of client devices in a Basic Service Set(BSS) having a mixture of physical (PHY) layer capabilities based ontheir version or type. For example, as shown in FIG. 1, the clientdevice (CD) 20(1) is an 802.11a/g device (called Type 1), CD 20(2) is an802.11n device (called Type 2), CD 20(3) is an 802.11ac device (calledType 3) and CD 20(N) is a 802.11ac device. In other words, the AP 10 isconfigured to serve a plurality of CDs such that at least one CD has ahigher bandwidth capability with respect to downlink transmissions sentby the AP 10 in two or more adjacent channels bonded together and atleast one other CD served by the AP 10 has lower bandwidth capabilitywith respect to downlink transmission sent by the AP 10 in a singlechannel or in two or more adjacent channels bonded together.

Reference is now made to FIG. 2. FIG. 2 illustrates a spectrum usagediagram for a BSS with a mixture of different types of CDs. This diagramshows that legacy CDs, such as 802.11a devices, use a small portion ofthe spectrum (e.g., 20 MHz) with a 64 quadrature amplitude modulation(QAM) scheme at reference numeral 30 whereas an 802.11ac device whichuses 80 MHz of the available spectrum with a 256 QAM scheme as shown areference numerals 32 and 34. Also, an 802.11n device uses as much as 40MHz of the spectrum with a 64 QAM scheme as shown at reference numeral36. The duration of an 802.11ac downlink transmission can be up to a fewmilliseconds, and comparable to the duration for an 802.11a/g/ntransmission, yet the 802.11a/g/n devices are still only using a smallportion of the available spectrum. Likewise, an 802.11n device uses alarger portion of the spectrum than an 802.11a device. Thus, in an 80MHz BSS, 60 MHz of bandwidth is wasted for legacy 802.11a devices and 40MHz of bandwidth is wasted for legacy 802.11n devices. In general, an802.11ac AP will be working at far below its rated capabilities wheneverthere are 802.11a and 802.11n transmissions occurring in the BSS.

The AP resources are underutilized and its capabilities are wasted formuch of the time. This underutilization reduces a user's motivation toupgrade the AP to a newer 802.11 protocol and consequently to upgradeCDs.

The way that a mixed BSS has been managed using current techniques is tohave the AP use a medium access control (MAC) address to protect thespectrum for use by the various types of CDs. This does not improve theutilization of the spectrum and in fact decreases efficiency.

According to the techniques described herein, the AP is configured tore-allocate its usage of the channels in its available frequencyspectrum to better serve the different types of CDs (CDs of differentbandwidth capabilities) in a mixed BSS. In a network deployment in whichthere is one or more device capable of higher bandwidth, there are waysto recover the wasted bandwidth by taking advantage of orthogonalfrequency divisional multiple access (OFDMA)-like schemes used fordownlink (DL) transmissions. The techniques described herein employmultiplexing in the frequency dimension.

Turning now to FIG. 3, an example block diagram is described of the AP10 that is configured to perform the improved spectrum utilizationtechniques described herein. The AP 10 comprises a controller 12, anetwork interface 14 for wired network communications, memory 16, awireless receiver 17, and a plurality of wireless transmitters18(1)-18(K). The AP 10 also comprises one or more antennas 19(1)-19(M).While only a single wireless receiver 17 is shown, this is by way ofexample only and in fact only one receiver is required. However, it ispossible that the AP 10 may have multiple receivers. Moreover, it ispossible that a single transmitter may be used to perform the functionsof the plurality of transmitters 18(1)-18(K). Thus, for simplicity, theblock of transmitters 18(1)-18(K) may be implemented by at least onetransmitter.

The WLAN receiver 17 performs the necessary baseband signal demodulationas well as radio frequency (RF) receive processing for WLANcommunications, and to this end, comprises, one or more integratedcircuit (IC) chips for these functions. The multiple wirelesstransmitters 18(1)-18(K) are each capable for performing the necessarybaseband signal modulation and RF transmit process functions. Thecontroller 12 is, for example, a microprocessor or microcontroller, oralternatively is a programmable digital signal processor, or a fixed orprogrammable digital logic device.

The memory 16 stores data that is used by the controller 12 forcontrolling functions of the AP 10. In addition, the memory 18 storesinstructions for AP control process logic 50 that, when executed by thecontroller 12, cause the controller to perform the operations describedherein in connection with FIG. 4 and the techniques depicted in FIGS.5-8. Thus, the memory 16 is an example of a tangible processor orcomputer readable memory medium that stores instructions which, whenexecuted by a processor, cause the processor to perform the spectrumallocation operations for the AP described herein when the AP sendsdownlink transmissions to CDs.

The techniques described herein are designed such that the AP 10 isconfigured to be transmitting or receiving, but never bothsimultaneously. In addition, the AP has multiple transmitters but needsonly a single receiver capable of receiving on one of a plurality ofchannels at any time. The AP can use single MAC contention techniques.

Reference is now made to FIG. 4 for a description of the AP controlprocess logic 50. At 52, the AP determines the nature of its mixed BSSthat it is serving, that is, the various types of client devices andfrom this information determines the spectrum usage capabilities, i.e.,a) bandwidth capabilities of the CDs that it the AP is serving, and b)support for the DL-OFDMA mechanism (e.g. IEEE 802.11ac and futuredevices) described herein. When a client device associates to the AP,the AP learns through uplink transmissions received from the CDs (whenthey initially associate to the AP), with which version of the IEEE802.11 standard the CD is compliant. For example, at 52, the AP learnswhether there are 802.11a devices, 802.11n devices, 802.11ac devices,etc., operating in the BSS that the AP is serving. Also, the AP willknow the protocol compliance/capability for each specific CD, and storesthis information indexed by a client device identifier. For example, atleast one CD served by the AP is capable of DL-OFDMA and has a higherbandwidth capability with respect to downlink transmissions in onechannel or several adjacent channels bonded together and at least onewireless client device has a lower bandwidth capability with respect todownlink transmissions in one channel or several adjacent channelsbonded together.

At 54, the AP generates control parameters for use of the bandwidthavailable to the AP to best serve the various types of client devices.Prior to generating the control parameters, the AP may contend for thebandwidth to determine availability of a plurality of channels fordownlink transmissions so that the control parameters are based theplurality of channels determined to be available to the AP at the timethe AP contends for the bandwidth for a downlink transmission intervalor session. The control parameters comprise information indicatingchannel assignments for multiple downlink transmissions that at leastpartially overlap in time to different CDs according to their respectivecapabilities and, in one form, information indicating timing fortransmissions of acknowledgment (ACK) messages by CDs to the AP.

In one form, ACK messages for the higher bandwidth CDs need not bescheduled and the techniques described herein allow for a polled ACKmechanism. In a polled ACK mechanism, the AP subsequently contends foraccess to the channel and requests an ACK message, e.g., via a Block ACKRequest (BAR) and the CD responds, e.g., with a BA. The AP polls each CDin turn for an acknowledgment.

At 56, the AP transmits the control parameters in a control frame inadvance of the downlink transmission interval. The control frame alertsthe higher bandwidth CDs that are part of the DL transmission intervalthat understand the DL-OFDMA mechanism (e.g., 802.11ac CDs) as to whichchannel(s) to receive their DL transmission(s) and, in one form, alsowhen to send their respective ACK messages. CDs that do not support theDL-OFDMA mechanism, e.g., 802.11a and 802.11n CDs continue to listen forpackets sent in their various operating channels that include a primarychannel. At 58, the AP receives ACK messages from the CDs that were partof the downlink transmission interval at the appropriate times asdescribed hereinafter. The control parameters, how they are transmittedand examples for the timing of the ACK messages are describedhereinafter in connection with FIGS. 5-8. The term ACK used herein ismeant to refer to an acknowledgment message of any type, including astandard acknowledgment message sent by a client device in response toreceiving an individual packet unit as well as a Block Acknowledgment(BA) which is transmitted to acknowledge multiple packet units together.Reference is also made herein to a so-called “fake” downlink ACK that istransmitted by the AP, which is described hereinafter.

Reference is now made to FIG. 5 for a first example of the controlparameters that the AP transmits to the client devices in its BSS. Inthis example, there are a first (primary) channel CH1, a second(secondary) channel CH2, a third channel CH3 and a fourth channel CH4,each 20 MHz wide for example. Also in this example the AP determinesthat there are two types of devices that it has frames for: 802.11ac and802.11n. At 60, the AP contends for the entire or some designatedportion of the bandwidth that is available to it (e.g., 80 MHz) andgains it. Any now known or hereinafter developed multi-channelcontention mechanism may be used by the AP at 60 that tends to minimizecollisions and maximizes fairness and throughput.

Next, the AP sends a control frame (CF) 100. The control frame 100contains information for the various client devices as to which one ormore of the four channels to expect their transmissions for a given DLtransmission interval or session shown at reference numeral 70.

The AP transmits the control frame 100 on each of the four channels asshown in FIG. 5. Moreover, as explained further in connection with FIG.6, the Physical Layer Convergence Protocol (PLCP) header in each DL802.11ac packet 115 to an 802.11ac CD indicates the subchannels of eachframe in the DL-OFDMA Transmit Opportunity (TXOP). A TXOP is a timeinterval obtained, through contention techniques, for transmissions by adevice, such as DL transmissions by the AP during a DL transmissioninterval.

The AP 10 can configure the control frame 100 to set different NetworkAllocation Vectors (NAVs) per subchannel, otherwise the control framecontents are the same and comprises a) a duration to end-of-legacy-ACK(EOLA) for ACK scheduling, the duration to the EOLA ACK represented bythe arrow 110 in FIG. 5 (omitted, if polled ACKs are always used; or setto 0 as a flag that polled ACKs are requested here, if both scheduledand polled ACKs are allowed), and b) subchannel assignments by CDidentifier which is an Association identifier (AID) assigned by the APto a CD, and represented by the arrows at reference numeral 112.

Still referring to FIG. 5, the control frame 100, in this example,indicates that the third and fourth channels are being bonded togetherfor a single DL packet to an 802.11ac client device with CD identifier(AID)=“x”. Client device “x” will then know to receive its transmissionon the third and fourth channels (bonded together). The control frame isbroadcasted at a basic rate for legacy CDs (a low rate understood by allCDs in the BSS), which in this example, assuming no nearby 802.11adevices, is the rate for 802.11n devices.

The 802.11n DL packet shown at 114 is the legacy frame in the example ofFIG. 5 and in this example the AP sends the legacy DL packet 114 on thefirst and second channels bonded together. However, the AP does notinclude any information in the control frame 100 about the legacy frameon the first and second channels because, again, the control frame 100is intended for decoding by higher bandwidth CDs (e.g., 802.11ac CDs)and 802.11a and 802.11n CDs do not understand and thus ignore thecontrol frame 100. Typically the 802.11n CD is the device with theslowest data rate and/or lower bandwidth capability among the CDs thatare destinations for a DL transmission during the DL transmissioninterval. The legacy DL frame 114 needs to be the longest frame in theDL transmission interval so all DL transmissions end before ACKreception begins. This significantly simplifies AP hardwareimplementation. The ACK message to be sent by a legacy CD and othernon-legacy CDs that are destinations for DL transmissions are to be sentin sequential order thereafter on the first subchannel as describedhereinafter.

The DL packet to 802.11ac CD is shown at 115 is transmitted on the thirdand fourth channels. In one form, the control frame 100 is furtherconfigured to cause the higher bandwidth 802.11ac CD “x” (referred to as“STA-x” in FIG. 5) to send its BA shown at 118 after the legacy CD sendsits ACK at 116 via the duration to the EOLA ACK 110. On the other hand,11a/11n CDs do not understand the control frame and immediately send anACK automatically (in the case of 802.11a) or if requested by a legacydata packet (as is the case for certain 802.11n frames). Thus, asdepicted in FIG. 5, the control parameters in the control frame indicatechannel assignments that result in multiple downlink transmissions todifferent client devices that at least partially overlap in time duringa downlink transmission interval according to the respective bandwidthcapabilities of the different client devices. In one form, informationis included in the control parameters to indicate the timing fortransmissions of ACK messages by the higher bandwidth DL-OFDMA capableclient devices to the AP. The control parameters indicate, during thedownlink transmission interval, that a downlink transmission will besent in one channel or several adjacent channels bonded together to atleast one wireless client device that has a higher bandwidth capability.

As an alternative to the sequencing of ACK messages, a time intervalpadding may be used on the non-primary channels (the second, third andfourth channels) and the ACK messages are frequency division multiplexedor sent sequentially on the non-primary channels after the DLtransmissions on the non-primary channels are completed.

In general, it is implicit that all ACK messages to be transmitted byCDs that are the destination of a DL frame in the DL transmissioninterval are to be on a particular channel or channels (e.g., theprimary channel and the adjacent secondary channel) corresponding to achannel to be used for DL transmissions to CDs having lower bandwidthcapability that are part of the DL transmission session/interval.Moreover, information indicating a duration or time interval from theend of the control frame 100 to the completion of the ACK message fromthe CD having the lower bandwidth capability (e.g., the duration to EOLA110) is specified in the control frame. However, the AP may use polledACK techniques instead of scheduling ACKs using the duration to EOLAinformation 110 for the higher bandwidth CDs.

As explained above, the control frame 100 may be configured to set adifferent NAV per channel to protect the information for the DL framesand ACK messages. The NAV is the virtual carrier sensing mechanism usedwith wireless network protocols such as IEEE 802.11 and IEEE 802.16. Thevirtual carrier sensing is a logical abstraction which limits the needfor physical carrier sensing at the air interface in order to save powerand increased reliability. The MAC layer frame headers contain aduration field that specifies the transmission time required for theframe, in which time the medium will be busy. The stations listening onthe wireless medium read the duration field and set their NAV, which isan indicator for a station on how long it must defer from accessing themedium. Wireless stations are often battery powered, so in order toconserve power the stations may enter a power-saving mode. The stationsdecrement its NAV counter until it becomes zero, at which time theyawaken to sense the medium again. The NAV virtual carrier sensingmechanism is a prominent part of the CSMA/CA random access protocol usedwith IEEE 802.11 WLANs.

The spectrum allocation scheme depicted in FIG. 5 can be viewed as ascheme wherein the control parameters in the control frame includesinformation indicating channel assignment for downlink transmissions ina subset of the plurality of channels to one or more client deviceshaving the higher bandwidth capability while implicitly one or moredevices having the lower throughput capability receive downlinktransmissions in one or multiple channels bonded together in a differentsubset of the plurality of channels than the subset of channelsallocated for the downlink transmission to the higher bandwidth wirelessclient devices. The subset of the plurality of channels allocated forthe higher bandwidth client devices does not overlap with one or more ofthe plurality of channels used for a downlink transmission to a clientdevice having a lower bandwidth capability

A further feature of the control frame 100, which is optional, is forthe AP to transmit a so-called “fake” DL ACK shown at 120 to make forfair access to the channel for 802.11ac and 802.11n client devices.Non-802.11ac Overlapping BSS (OBSS) client devices will perform ExtendedInterframe Spacing (EIFS) after the DL packet 115. Thus, the fake DLACKs shown at 120 achieve fairness with 802.11ac OBSS client devices. Inthis way, 802.11n and 802.11ac client devices have an equal chance totransmit on the non-primary channels after the DL packet 115. The DLACKs shown at 120 are “fake” because it is understood that an AP doesnot normally send a DL ACK which is not actually acknowledging anything.The AP generates and transmits a DL ACK as a means to allow all clientdevices to decode it and therefore realize that the channel is occupiedso that they do not contend for it. Said another way, the AP transmitson the subset of channels allocated to a higher bandwidth CD messagesthat are configured as ACK messages to cause other devices that detectthe ACK messages (transmitted by the AP) to refrain from contending forthe subset of channels and after a period of time to allow forcontention to that subset of channels. Again, as explained above, thecontrol frame includes information to indicate that ACK messages fromthe one or more CDs having the higher bandwidth capability are to besent, in sequence by specific CD, subsequent the last ACK message fromthe one or more CDs having the lower bandwidth capability.

Furthermore, the AP generates the control parameters to schedule framesfor a lower bandwidth capability CD that are longer in duration than forframes for higher bandwidth CDs so that the AP need only transmit orreceive at any given time but not transmit and receive at the same time.

Turning now to FIG. 6, one example of the control frame 100 is shown.The control frame 100 comprises a Duration field 101, a first address(Address 1) field 102, a second address (Address 2) field 103, an EOLADuration field 104, a Number of subchannels fields field 105, and one ormore Subchannel fields 106(1)-106(N). Each Subchannel field 106(i)comprises a Subchannel ID field 107 and an AID subfield 108 and aReserved field 109.

The Duration field 101 specifies the time duration of the control framefrom start to finish. The control frame 100 is a variable length frame.A fixed length may be used up to 8 subchannels*4 AIDs/subchannel*1.5octets/AID=48 octets+20 MAC bytes.

The Address 1 field 102 specifies a Broadcast address for a given BSS sothat all CDs in the BSS receive and decode the control frame 100. TheAddress 2 field 103 specifies the BSS identifier (BSSID) for the BSSsince that is the target of the control frame 100. The EOLA Durationfield 104 indicates the time interval from the end of the control frame100 to the end of the legacy ACK frame as shown at 110 in FIG. 5.

The Number of subchannel fields field 105 indicates the number ofSubchannel fields 106(1)-106(N). In an alternative form, one Subchannelfield is used and the CDs can obtain the full list of subchannels fromthe PLCP header of the DL data frame. A DL frame sent to a given AIDacross N subchannels requires N subchannel fields. Within a givenSubchannel field 106(i), the Subchannel ID field 107 includesinformation that identifies a 20 MHz channel within up to 160 MHz ofbandwidth (e.g., using 3 bits). For example, one 40 MHz 11ac client uses27 octets or 60 μs at 6 Mbps (802.11a). This corresponds to theinformation represented by the arrows shown at 112 in FIG. 5. MultipleAIDs may be used per subchannel in order to support DL-Multi-UserMultiple-Input Multiple-Output (MIMO). As an alternative, there may beone subchannel ID field per CD. The AID subfield may be shortened toobtain additional bits for a larger subchannel ID field (a 4 or 8 bitbitmask with 1 bit per 20 MHz subchannel).

The control frame 100 is unsecured because, by its nature, it istransmitted shortly before the actual DL frames and thus there is notsufficient time to negotiate and transmit security information to theCDs. Providing for an unsecured control frame introduces the possibilityof a new type of denial of service attack on target clients. Theattacking device may regularly send a bogus control frame directingselected AIDs to a non-primary/secondary (little-used) subchannel andthen after a Short Interframe Spacing (SIFS), the attacking device sendsa long packet on the indicated subchannel.

During this attack, the selected client devices that are the target misspackets sent by the AP on the other subchannels, e.g., on theprimary/secondary subchannels. The attack requires the attacker totransmit more or less continuously. A target client device can mitigatethe attack as follows. If there is no energy on the primary channelafter the (SIFS), or energy on the primary channel disappears wellbefore EOLA Duration-SIFS-TXTIME (ACK or BA), then an attack can bedetermined to be occurring.

In general, the PLCP header of each DL packet/frame self-announces thesubchannels occupied by the packet. This self-announcement can be assimple as a 20/40/80/160 MHz indication, and thus 2 bits suffice. WithDL-OFDMA, an extension is possible wherein the number of bits depends onthe maximum bandwidth and minimum bonding assumed within DL-OFDMA for an802.11ac device. Options include:

1. One bit per subchannel, so that 80 MHz maximum requires 4 bits(1,2,3,4) but 160 MHz max requires 8 bits (1,2,3,4,5,6,7,8); or

2. With more bonding (aggregating) of the “higher” subchannels so that80 MHz maximum requires 3 bits (1,2,3+4) and 160 MHz max requires 5 bits(1,2,3+4,5+6,7+8).

FIG. 7 shows the sample encodings used in a DL-OFDMA transmission, fortwo 802.11ac CDs and one legacy CD. The AP covers a bandwidth of 160MHz, covering channels 36-64. The legacy CD automatically listens on theprimary channel (channel 36) and receives it legacy packet that way. Thefirst 802.11ac CD's data packet is on channels 44 and 48 bondedtogether, which is indicated by the encoding “00100” (i.e. 3+4 which is44+48 in this BSS) sent in the PLCP header of that data packet. Thesecond 802.11ac CD's data packet is on channels 52-64, which isindicated by the encoding “00011” (i.e. 5+6,7+8 which is 52+56 and 60+64in this BSS). The constraint that the legacy DL frame be the longestframe is not too restrictive. With aggregation of data units (in time)to be transmitted, the AP can lengthen an 802.11n frame withoutover-lengthening the 802.11ac frames. During early adoption of 802.11ac,802.11a/802.11n frames will dominate, so there is “always” a legacyframe for an 802.11ac data unit on which to “piggyback”. During thelatter stages of 802.11ac adoption, 802.11ac frames will dominate, sothere is “always” an 802.11ac data unit to transmit alongside slowerlegacy frames.

The spectrum allocation techniques described herein work for broadcastframes as well. Broadcast frames are sent on channels always includingthe primary channel, and not in parallel with DL-OFDMA frames during thesame TXOP.

In a variation, the transmission of the control frame could be avoidedby the AP pre-assigning selected client devices to different subchannelsfor reception purposes. For example, the primary channel becomes theprimary channel for transmission, but different client devices havedifferent primary channels for reception. This works well for unicasttransmissions, but broadcast transmissions need either to be duplicatedacross subchannels or the AP sends a control frame to temporarily moveclient devices back to the primary channel in order to receive broadcasttransmissions in much the same way as shown in FIG. 5, but with thecontrol frame including information pointing client device “x” from, forexample, the third subchannel back to the first subchannel to receive aDL broadcast packet on the primary channel.

FIG. 8 illustrates another example where the lower bandwidth legacyclient device is an 802.11a client device and there are three 802.11acclients (referred to as STA-x, STA-y and STA-z in FIG. 8) in the BSSthat are destinations during the DL transmission interval. In thisexample, both DL-OFDMA and DL-MUMIMO is used. There are six channels inthis example, denoted CH1, CH2, . . . , CH6.

The DL frame to the legacy (lower bandwidth) 802.11a CD is on theprimary channel (CH1) and shown at 214. The DL packet to the higherbandwidth CD “x” (STA-x) is on the secondary channel (CH2) and shown at216. The DL-MUMIMO packet to the higher bandwidth CDs “y” and “z” (STA-yand STA-z) is sent via MU-MIMO on the third and fourth bonded channels,and shown at 218. OBSS traffic is occurring on the fifth and sixthsubchannels and shown at 220. The ACKs from the four client devices thatare included in the DL transmission interval in this example all occuron the first channel and occur in order of the 802.11a ACK at 222 fromthe 802.11a client device, followed by the 802.11ac BA from STA-x at224, followed by the BA of the 802.11ac STA-y at 226 and finally the BAby the 802.11ac STA-z at 228. The AP may also send the optional “fake”DL ACKs as shown at 230, 232, and 234 on the second, third and fourthchannels.

In another example, the AP generates control parameters in the controlframe for a single user (SU) MIMO downlink transmission to a CD and fora MU-MIMO downlink transmission to multiple CDs. In other words, theDL-OFDA techniques described herein are consistent and capable ofsupporting both SU-MIMO and MU-MIMO transmissions.

The design of the PHY layer of the AP may be essentially the same as thestandards otherwise provide. One exception is that the AP may adaptivelyadjust power of downlink transmissions transmitted in different channelsaccording to data rate in order to meet rejection channel capabilitiesof different client devices. For example, legacy packets sent with 64QAM, ¾, or higher may be amplified by 1-2 dB with respect to 802.11acconstellation points so as not to exceed legacy specifications. Inanother variation, the AP may be configured to never to send packets atthe very highest modulation and coding schemes to legacy devices withina DL transmission interval, and only use modulation and coding schemeswith sufficiently tight requirements on adjacent channel interferencerejection. At the client device, the receiver can follow its usualprocess for start-of-packet detection, coarse carrier detection, etc.Indeed, the client device can continue to process the primary channel asusual even if its intended packet lies on one or more of the second,third or fourth channels because it will receive the same informationinitially on the primary subchannel as it would on the other channelsand therefore it need not immediately switch to the other channels.

The techniques described herein provide for an overall increase in thesingle-BSS bandwidth whenever non-primary frames are longer than thecontrol frame. This is particularly valuable with legacy client devicesin an 80 or 160 MHz BSS. The AP only needs to transmit or receive; itnever needs to be both transmitting and receiving simultaneously. The APonly needs to contend for the channel once; it does not need multipleMAC contentions to send to multiple CDs. The PHY filtering andprocessing performed by the AP and client devices is very similar toexisting MIMO-OFDM requirements and therefore can be done withoutspecial analog (e.g. converter or RF filtering) changes. Moreover, an APwith a single PHY receiver is still capable of performing the techniquesdescribed herein. The usage of non-primary channels is minimized so thatthey can be shared between BSS's.

In sum, a method is provided wherein, at a wireless network access pointdevice, control parameters are generated for usage of a plurality ofchannels in a bandwidth during a downlink transmission interval, thecontrol parameters comprising information indicating channel assignmentsthat result in multiple downlink transmissions that at least partiallyoverlap in time to different wireless client devices according to theirrespective bandwidth capabilities. In one form, the control parametersalso include information indicating timing for transmissions ofacknowledgment messages by higher bandwidth client devices to the accesspoint device. In advance of the downlink transmission interval a controlframe containing the control parameters is transmitted by the accesspoint device on each of the plurality of channels in the bandwidth.

In addition, an apparatus is provided comprising at least onetransmitter configured to transmit wireless signals in one or more of aplurality of channels in a bandwidth; and a controller configured to becoupled to the at least one transmitter. The controller is configured togenerate control parameters for usage of the plurality of channelsduring a downlink transmission interval, the control parameterscomprising information indicating channel assignments resulting inmultiple downlink transmissions that at least partially overlap in timeto different wireless client devices according to their respectivebandwidth capabilities; and supply to the at least one transmitter acontrol frame containing the control parameters for transmission inadvance of the downlink transmission interval on each of the pluralityof channels.

Further still, a processor readable medium is provided that storesinstructions that, when executed by a processor, cause the processor to:generate control parameters for usage of the plurality of channelsduring a downlink transmission interval, the control parameterscomprising information indicating channel assignments that result inmultiple downlink transmissions that at least partially overlap in timeto different wireless client devices according to their respectivebandwidth capabilities; and supply to at least one transmitter a controlframe containing the control parameters for transmission in advance ofthe downlink transmission interval on each of the plurality of channels.

The above description is by way of example only.

What is claimed is:
 1. A method comprising: at a wireless access pointthat serves at least first and second wireless devices having lower andhigher bandwidth capabilities, respectively: generating controlparameters including information that: assigns first and secondnon-overlapping channel bandwidths for first and second downlinktransmissions to the first and second wireless devices, respectively;and indicates timing for an acknowledgement to be sent from the firstdevice and after which an acknowledgement from the second device is tobe sent; transmitting a first downlink transmission to the first deviceover the first channel bandwidth at a lower data rate during a firsttime interval; transmitting a second downlink transmission to the seconddevice over the second channel bandwidth at a higher data rate during asecond time interval that partially overlaps with and ends at or beforethe first time interval; and transmitting a false acknowledgementmessage that does not acknowledge anything over the second bandwidthafter the second time interval and during the first time interval. 2.The method of claim 1, wherein the wireless access point serves thefirst device having the lower bandwidth capability and one or moresecond devices having the higher bandwidth capability, and thegenerating includes generating control parameters including informationto indicate that acknowledgement messages are to be sent from the one ormore higher bandwidth second devices in sequence after theacknowledgment from the lower bandwidth first device.
 3. The method ofclaim 2, further comprising, at the wireless access point, receivingacknowledgements from the lower bandwidth first device and the one ormore higher bandwidth second devices over the first channel bandwidthassigned to the lower bandwidth first device.
 4. The method of claim 3,wherein: the generating includes generating the control parameters toinclude information that assigns one or more second non-overlappingchannel bandwidths that do not overlap with the first channel bandwidthfor downlink transmissions to the one or more higher bandwidth seconddevices.
 5. The method of claim 1, wherein: the generating includesgenerating control parameters including information to assign the secondchannel bandwidth to the higher bandwidth second device as multiplecontiguous channels selected from a set of available channels and bondedtogether; and the transmitting the false acknowledgement includestransmitting the false acknowledgement over the multiple contiguouschannels bonded together.
 6. The method of claim 1, wherein thetransmitting a second downlink transmission including transmitting aphysical layer convergence protocol (PLCP) header in the downlinktransmission including a field to identify channels selected from amonga set of channels and assigned to the second device, the field includingbits encoded so that three bits represents a bandwidth of 80 MHz andfive bits represents a bandwidth of 160 MHz.
 7. The method of claim 1,further comprising, at the wireless access point, determining therespective bandwidth capabilities of the different devices, wherein thedetermining includes determining the lower bandwidth first device is alegacy device that operates in accordance with one of an IEEE 802.11aand 802.11n standards and the higher bandwidth device operates inaccordance with an IEEE 802.11ac standard.
 8. The method of claim 1,further comprising polling at least one of the at least first and seconddevices for acknowledgements and receiving at least one polledacknowledgements from the at least one of the first and second polleddevices.
 9. An apparatus comprising: at least one transmitter and areceiver respectively configured to transmit wireless signals to andreceive signals from different wireless devices having differentrespective bandwidth capabilities; and a controller configured to becoupled to the at least one transmitter and the receiver, wherein thecontroller is configured to: generate control parameters based on thedifferent bandwidth capabilities, the control parameters includinginformation that: assigns first and second non-overlapping channelbandwidths for first and second downlink transmissions to first andsecond devices having lower and higher bandwidth capabilities,respectively; and indicates timing for an acknowledgement to be sentfrom the first device and after which an acknowledgement from the seconddevice is to be sent; cause the at least one transmitter to transmit afirst downlink transmission to the first device over the first channelbandwidth at a lower data rate during a first time interval; cause theat least one transmitter to transmit a second downlink transmission tothe second device over the second channel bandwidth at a higher datarate during a second time interval that partially overlaps with and endsat or before the first time interval; and cause the at least onetransmitter to transmit a false acknowledgement message that does notacknowledge anything over the second bandwidth after the second timeinterval and during the first time interval.
 10. The apparatus of claim9, wherein the at least one transmitter is configured to transmitsignals to the first device having the lower bandwidth capability andone or more second devices having the lower bandwidth capability, andthe controller is configured to generate by generating controlparameters including information to indicate that acknowledgementmessages are to be sent from the one or more higher bandwidth seconddevices in sequence after the acknowledgment from the lower bandwidthfirst device.
 11. The apparatus of claim 10, wherein the controller isfurther configured to receive acknowledgements from the lower bandwidthfirst device and the one or more higher bandwidth second devices overthe first channel bandwidth assigned to the lower bandwidth firstdevice.
 12. The apparatus of claim 11, wherein: the controller isconfigured to generate by generating the control parameters to includeinformation that assigns one or more second non-overlapping channelbandwidths that do not overlap with the first channel bandwidth fordownlink transmissions to the one or more higher bandwidth seconddevices.
 13. The apparatus of claim 9, wherein: the controller isconfigured to generate by generating control parameters includinginformation to assign the second channel bandwidth to the higherbandwidth second device as multiple contiguous channels selected from aset of available channels and bonded together; and the controller isconfigured to cause the at least one transmitter to transmit by causingthe transmitter to transmit the false acknowledgement includestransmitting the false acknowledgement over the multiple contiguouschannels bonded together.
 14. The apparatus of claim 9, wherein thecontroller is configured to cause the at least one transmitter totransmit by causing the at least one transmitter to transmit a seconddownlink transmission including transmitting a physical layerconvergence protocol (PLCP) header in the downlink transmissionincluding a field to identify channels selected from among a set ofchannels and assigned to the second device, the field including bitsencoded so that three bits represents a bandwidth of 80 MHz and fivebits represents a bandwidth of 160 MHz.
 15. The apparatus of claim 9,wherein the controller is further configured to determine the respectivebandwidth capabilities of the different devices, wherein the determiningincludes determining the lower bandwidth first device is a legacy devicethat operates in accordance with one of an IEEE 802.11a and 802.11nstandards and the higher bandwidth device operates in accordance with anIEEE 802.11ac standard.
 16. A non-transitory computer readable mediumstoring instructions that, when executed by a processor, cause theprocessor to: at a wireless access point that serves different wirelessdevices having different respective bandwidth capabilities, generatecontrol parameters based on the different bandwidth capabilities, thecontrol parameters including information that: assigns first and secondnon-overlapping channel bandwidths for first and second downlinktransmissions to first and second devices having lower and higherbandwidth capabilities, respectively; and indicates timing for anacknowledgement to be sent from the first device and after which anacknowledgement from the second device is to be sent; cause atransmitter to transmit a first downlink transmission to the firstdevice over the first channel bandwidth at a lower data rate during afirst time interval; and cause the transmitter to transmit a seconddownlink transmission to the second device over the second channelbandwidth at a higher data rate during a second time interval thatpartially overlaps with and ends at or before the first time interval;and cause the transmitter to transmit a false acknowledgement messagethat does not acknowledge anything over the second bandwidth after thesecond time interval and during the first time interval.
 17. Thenon-transitory computer readable medium of claim 16, wherein thewireless access point serves the first device having the lower bandwidthcapability and one or more second devices having the higher bandwidthcapability, and the instructions to cause the processor to generateinclude instructions to cause the processor to generate controlparameters including information to indicate that acknowledgementmessages are to be sent from the one or more higher bandwidth seconddevices in sequence after the acknowledgment from the lower bandwidthfirst device.
 18. The non-transitory computer readable medium of claim17, further comprising instructions to cause the processor to receiveacknowledgements from the lower bandwidth first device and the one ormore higher bandwidth second devices over the first channel bandwidthassigned to the lower bandwidth first device.
 19. The non-transitorycomputer readable medium of claim 18, wherein: the instructions to causethe processor to generate include further instructions to cause theprocessor to generate the control parameters to include information thatassigns one or more second non-overlapping channel bandwidths that donot overlap with the first channel bandwidth for downlink transmissionsto the one or more higher bandwidth second devices.
 20. Thenon-transitory computer readable medium of claim 16, wherein: theinstructions to cause the processor to generate include instructions tocause the processor to generate control parameters including informationto assign the second channel bandwidth to the higher bandwidth seconddevice as multiple contiguous channels selected from a set of availablechannels and bonded together; and the instruction to cause the processorto cause the transmitter to transmit the false acknowledgement includeinstructions to cause the processor to cause the transmitter to transmitthe false acknowledgement over the multiple contiguous channels bondedtogether.